1. Field of the Invention
This invention relates to apparatus for enclosing exciter collector sets on turbine driven electric power generators, and more particularly to such apparatus with improved ventilation for the collector rings and brushes, and with features which permit the collector brushes to be changed with the generator at full load.
2. Background Information
Large turbine generators with static excitation utilize collector sets for conducting current to the rotor. The collector sets comprise a pair of collector rings, one for each polarity, mounted on the rotor and a set of stationary brushes angularly displaced around, and in contact with, each collector ring. In order to protect the collector sets and to prevent inadvertent contact with them by personnel, the collector sets are enclosed within an enclosure which includes a fixed base. In order to provide ventilation within the enclosure to cool the collector sets, a centrifugal fan is typically mounted on the rotor shaft within the enclosure to draw air into the enclosure through openings in the base and to exhaust the cooling air through an exhaust stack in the roof of the enclosure.
Typically, the collector set enclosure includes stationary transverse end walls with sealed openings through which the rotor shaft passes, and a removable U-shaped housing defining the roof and side walls of the enclosure. While the housing can be removed for maintenance either by sliding it horizontally or lifting it vertically, in some installations it is desirable to be able to change the brushes without shutting the generator down. Accordingly the housing may be provided with doors through which access may be gained to the collector set. In some generators/having large numbers of brushes, several brushes are mounted in insulated cartridges which can be removed and replaced through the access door while the unit is in operation. Since hundreds of amperes of current can be flowing through the collector sets, it is important that contact not be made with both polarity units or with the collector set and a grounded conductor at the same time.
The increase in the operating temperature of the collector set resulting from the fact that it is enclosed reduces its efficiency. It is desirable therefore to provide improved ventilation for the collector set to improve its rating. It is also desirable to improve the ventilation so that the size of the enclosure can be reduced. At the same time, it is in some instances desirable to have such an enclosure with improved ventilation and reduced size which permits safe changing of brushes while the generator is in operation.